Thermal cycler having a temperature analysis and/or verification unit and a method for analyzing or verifying a thermal performance of a thermal cycler and for calibrating the thermal cycler

ABSTRACT

The invention relates to a thermal cycler ( 10 ) comprising a housing ( 12 ), the housing ( 12 ) accommodating a thermal block ( 14 ) having a plurality of sample wells ( 32 ), each for receiving a test sample in a sample vessel, electric heater means ( 18 ) for heating the thermal block ( 14 ), a power supply ( 24 ) and an electronic control ( 22 ) for controlling the electric heater means ( 18 ), and further comprising a temperature analysis and/or verification unit ( 28 ) for analyzing and/or verifying a thermal performance of the thermal block ( 14 ). The invention further relates to a method for analyzing or verifying a thermal performance of a thermal cycler ( 10 ) and for calibrating the thermal cycler ( 10 ). The thermal cycler ( 10 ) is characterized in that the temperature analysis and/or verification unit ( 28 ) is integrated into the housing ( 12 ) and is connected to the power supply ( 24 ) and to the electronic control ( 22 ) by means of an internal interface ( 26 ), whereas the method is characterized by the following steps: providing the thermal cycler ( 10 ) with an integrated temperature analysis and/or verification unit ( 28 ) and using the integrated temperature analysis and/or verification unit ( 28 ) for self-calibration of the thermal cycler ( 10 ).

This application is a continuation of U.S. Ser. No. 15/103,543, now U.S.Pat. No. 10,307,762 filed Jun. 10, 2016, which is a national stageapplication of International Application No. PCT/EP2014/076158, filedDec. 2, 2014, which claims priority from European Patent Application No.13196781.2, filed Dec. 12, 2013, from which applications priority isclaimed, and which all are incorporated herein by reference.

This invention relates to thermal cyclers. Specifically, the presentinvention is directed to a thermal cycler having a temperature analysisand/or verification unit according to the preamble of claim 1. Thepresent invention is further directed to a method for analyzing orverifying a thermal performance of a thermal cycler and for calibratingthe thermal cycler according to the preamble of claim 12. In additionthe present invention relates to a use of the thermal cycler and themethod according to claim 15.

STATE OF THE ART

A thermal cycler (also known as a thermocycler, PCR machine or DNAamplifier) is a laboratory apparatus most commonly used to amplifysegments of DNA via the polymerase chain reaction (PCR), which is nowcommon place within Molecular Biology, in both Research and Diagnosticssectors. However thermal cyclers may also be used in laboratories tofacilitate other temperature-sensitive reactions, including but notlimited to restriction enzyme digestion or rapid diagnostics. Thermalcyclers are generally equipped with a thermal block having an array ofsample wells or holes where tubes or other vessels holding the testsamples can be inserted. Quality thermal cyclers often contain silverblocks to achieve fast temperature changes and uniform temperaturethroughout the block. After the insertion of the vessels into the samplewells or holes the temperature of the thermal block is raised andlowered in discrete, pre-programmed steps for alternately heating andcooling the test samples during the cycles of the PCR. In case of apoorly performing thermal cycler where the temperature of the thermalblock is not uniform or where the thermal block is not heated or cooledaccording to an exact predetermined target temperature curve there is apotential to, for example, provide false-negative PCR results.

In order to ensure a consistent and accurate thermal performance ofthermal cyclers, i.e. thermal uniformity of the thermal block orwell-to-well uniformity, temperature accuracy, heating and coolingrates, temperature overshoot and timing, it is necessary to analyze orverify these parameters and eventually to calibrate the thermal cyclersin case of a poor thermal performance.

At present there are three possible alternatives available to the userfor analysis or verification of thermal cycler thermal performance:

1. Manufacturer Service Contract

Here the users opt for a service agreement with the actual manufacturerof the thermal cycler. A test engineer from the manufacturer visits theusers and performs a verification test on-site.

Although the true cost of this exercise is often difficult to determine,as it is typically included within the purchase price of the thermalcycler, it can be expensive. Costs should be considered on acase-by-case basis.

Typically manufacturers recommend performing this test on an annualbasis, a frequency of verification typically not commensurate with mostquality control requirements because thermal cycler performance couldbegin to degrade immediately following any on-site check.

Even though eventually a calibration of the thermal cycler is possibleand adjustments can be made to the temperature if required, because themanufacturer's test engineer has intimate knowledge of themanufacturer's thermal cyclers, there are quite a few drawbacksassociated with manufacturer service contracts:

When the on-site verification is performed by an external/visiting testengineer the testing must be well organized as all the manufacturer'sthermal cyclers on site must be available for verification within aspecified period. During this period the thermal cyclers are notavailable for PCR.

Often on-site verification contracts are only commercially suited forsites which have many thermal cyclers to test as the costs of having anengineer visit to verify only one or few thermal cyclers would typicallyprove prohibitive.

Maintaining a history record of each thermal cycler is very difficult.Such a history record will typically involve a manual comparison oftext-based test reports, where the users themselves have to pick-out outpertinent data and then have to manually enter the data into aspreadsheet-type application for comparison.2. Verification Using Purchased Test Equipment

In this instance the users purchase a piece of proprietary temperaturetest equipment and perform the verification testing themselves.Naturally there is a significant financial investment required with thisapproach, particularly when considering the wide array of test equipmentthat may require purchasing to ensure compatibility with the variousmakes and models of thermal cyclers that require testing.

Often the test equipment purchased is identical to that utilized fortesting carried out under manufacturer service contracts. However thetraining required to operate this equipment correctly, in a manner thatwill achieve accurate, repeatable and meaningful results, is seldomaccessible. In addition interpretation of the results is often verysubjective. Typical test equipment is designed to be operated by trainedpersonnel—often requiring a specific skill set to obtain satisfactoryand valid test results.

Pass fail limits are typically not provided with the test equipment asthis causes friction between the manufacturer, the test equipmentsupplier and the user. How can a user be expected to achieve the sametest results as those the manufacturer achieves in a fully controlledenvironment with their own different, dedicated test equipment.

Furthermore manufacturers are reluctant at best to pass on details oftesting procedures, making comparison against published specificationsall but impossible. Where pass/fail thermal performance limits areavailable then they tend to be supplied in the form of wider-tolerance“field limits”. These limits naturally lead to confusion as they aredifferent to published specifications in every regard.

The issue of how to perform the test now comes into question;inconsistencies in test protocols, apparatus and methodology are allvariables that can skew results.

The selection and purchasing of the correct test equipment is an issue,sometimes the configuration of a “correct test system” can be extremelydifficult.

Often the systems available for purchase are particularly complex inoperation, having to cater for many different makes and models.

Although this method allows the user to conduct a thermal test onthermal cyclers, in case of a discrepancy their calibration is often notpossible. Should calibration be required the discrepancy has to bereported to the manufacturer. The manufacturer then has to confirm theresults, a process often causing friction with respect to publishedspecification etc, and then an engineer has to visit the site or thethermal cycler in question has to be returned to the manufacturer forcalibration.

Often the user has no alternative other than to simply leave the thermalcycler unadjusted, despite knowing that its thermal performance is poor.

Maintaining a history record of the unit is again very difficult; thistypically will involve a manual comparison of text-based test reports,where the users themselves have to pick-out out pertinent data and thenhave to manually enter the data into a spreadsheet-type application forcomparison.

3. Using a Thermal Cycler Servicing Company

Here the users can contract-out the job of thermal cycler verificationto a third party thermal cycler servicing company that specializes inthermal cycler temperature verification. As with the manufacturerservice contract a test engineer typically visits the customer andperforms the verification testing on-site. If the user has manydifferent makes and models of thermal cyclers that require validationthis solution does offer cost advantages as it makes little sense forthe user to purchase all the different variations of test equipment thatare available.

Thermal cycler servicing companies generally offer a more detailedverification of thermal performance compared to that provided as part ofa manufacturer's service contract. However the test equipment used isnot necessarily well suited to the specific thermal cycler being testedand manufacturers will disregard any test data yielding from anon-approved source.

In addition thermal cycler servicing companies generally utilize thetest equipment that is available for purchase by the end user. Thereforethe same limitations apply as for the validation using purchased testequipment.

In the unusual event of the servicing company having the technicalknow-how to re-calibrate the thermal cycler it remains that in mostinstances this process will invalidate any warranty on the instrument.

Maintaining a history record of the unit is again very difficult; thistypically will involve a manual comparison of text-based test reports,where the users themselves have to pick-out out pertinent data and thenhave to manually enter the data into a spreadsheet-type application forcomparison.

Therefore none of the methods cited above provide a wholly satisfactorysolution for the user.

The external test equipment used in the methods cited above generally isin the form of a temperature analysis and/or verification unit thatcomprises a temperature probe plate with a plurality of temperatureprobes and further comprises a separate external control unit thatcommunicates with the temperature probes of the probe plate and isequipped with a power supply, a processor for controlling thetemperature analysis and/or verification process as well as a memory anda display for storing or displaying the test results respectively.

DETAILED DESCRIPTION OF THE INVENTION

It is therefore an object of the present invention to provide a thermalcycler and a method for verifying a thermal performance of a thermalcycler and for calibrating the thermal cycler that will avoid or atleast ameliorate the above mentioned drawbacks.

In order to achieve these objects the present invention provides athermal cycler according to claim 1 and a method for verifying a thermalperformance of a thermal cycler and for calibrating the thermal cycleraccording to claim 12. Furthermore the present invention provides theuse of such a thermal cycler and/or method for Polymerase Chain Reaction(PCR).

The thermal cycler and method according to the invention provide thefollowing advantages:

-   -   Temperature verification: The temperature analysis and/or        verification unit does not only provide validation, i.e. that        the thermal cycler is operational, but also verification, i.e.        that the temperatures achieved in the samples wells are        according to specification.    -   Self Calibration: The results generated by the integrated        temperature analysis and/or verification unit can be directly        used to verify the thermal performance of thermal cycler and, if        necessary, to allow the thermal cycler to automatically        calibrate itself.    -   Frequency of Test: Analyses and/or verification of the thermal        performance of the thermal block can be performed as frequently        as desired with no additional cost penalties. Annual tests can        be replaced with weekly or even daily checks.    -   Usability: The integrated temperature analysis and/or        verification unit is specifically designed for use with the        specific thermal cycler and can be easily adapted to different        thermal block designs used on the Thermal Cycler. The thermal        cycler can have a simple, bespoke design, where no formal        training is required for foolproof operation.    -   The integrated temperature analysis and/or verification unit        verification system can be made identical to the temperature        analysis and/or verification unit that is used for quality        control at the manufacturer which ensures that data is directly        comparable. The calibration procedure can be also made identical        to the calibration procedure used by the manufacturer for        quality control so that the pass/fail limits being similarly        identical.    -   The thermal cycler itself maintains its own history which allows        for automatic lifetime monitoring/trend analysis of all key        thermal performance values, all results being stored onboard        electronically in a memory of the thermal cycler's electronic        control or in a memory of the integrated temperature analysis        and verification unit. No manual interpretation is required by        the user as the results can be electronically retrieved or        indicated on a display of the thermal cycler on demand.    -   The level of thermal validation is fully controllable by the        user, ranging from quick “health checks” to a fully in-depth,        detailed analysis.    -   A baseline can be set by the user, either typical        PCR-temperatures or temperatures that are of particular interest        to the user, and the variation from which can be analyzed when        required. This allows the user to instantly spot any deviation        in performance away from the norm.

Compared to a manufacturer service contract where a test engineer fromthe manufacturer performs temperature verification tests on-site thereis no need to thoroughly organize the tests as they can be performedwhenever need arises and can be independently performed for each thermalcycler so that downtime of a large number of thermal cyclers can beavoided.

Compared to the verification using purchased test equipment anintegrated temperature verification and calibration unit will always becustomized or tailor-made for the thermal cycler with which it is used.If necessary, the training required to operate the integratedtemperature verification in a manner that will achieve accurate,repeatable and meaningful results, will be provided by the manufacturerof the thermal cycler together with the training to operate the thermalcycler itself. Therefore there will be no questions how to perform thetest and how to adapt test equipment to a particular thermal cycler.This will generally result in satisfactory and valid test resultswithout any inconsistencies in test protocols.

Compared to the use of a thermal cycler servicing company the testequipment used is perfectly suited to the specific thermal cycler beingtested because it has been developed and undergone quality controltogether with that specific thermal cycler. Due to the fact that theintegration of the temperature verification and calibration unit intothe thermal cycler will be generally performed during the manufacture ofthe thermal cycler any test data will yield from a source approved bythe manufacturer and calibration will not invalidate any warranty on theinstrument.

Probably most important compared is the ability for self-calibrationwhich in not possible in any of the three alternatives presently athand.

According to a preferred embodiment of the invention the integratedtemperature analysis and/or verification unit comprises a temperatureprobe plate having a plurality of temperature probes for measuring thetemperature within selected sample wells. Such temperature probe plateshave already proven reliable in exterior test equipment used for theverification of thermal performance of thermal cyclers. Preferably thetemperature analysis and/or verification unit comprises a closed loopcontrol for calibration of the electric heater means in dependency ofthe temperature measured by the temperature probes within selectedsample wells.

When not in use, i.e. during normal operation or downtime of the thermalcycler, the temperature probe plate is preferably stowed on the thermalcycler itself and most preferably accommodated within a stowagecompartment of the housing from where it can be removed and placed onthe thermal block for performing a temperature analysis and/orverification, when required. The opening of the stowage compartment isadvantageously located on top of the housing close to the thermal blockand the sample wells for easy access to the probe plate, when required.

According to a first alternative the temperature probes are fixed to thetemperature probe plate so that they are always associated with specificsample wells. According to a second alternative the temperature probesare variable probes that are interchangeable and can be selectivelyattached to different sockets of the temperature probe plate so thatthey can be used to verify or calibrate different sample wells. This isadvantageous to tackle specific requirements, for example a detailedthermal gradient analysis or a verification or calibration of a specificarea of the sample wells that is giving atypical performance. The latteralternative also provides for non-standard block or well dimensions orfor the attachment of leaded probes to the sockets of the temperatureprobe plate.

According to a further preferred embodiment of the invention all thetemperature probes carry their own unique identity which isautomatically recognized by software in the thermal performance analysisand/or verification unit. This will ensure integrity of temperature datafrom one test to the next, regardless of the position of the temperatureprobe on the probe plate or in one of the sample wells respectively.

Preferably the temperature probe plate is connected to the internalinterface by mating electrical contacts or by an electrical plug-inconnection when the temperature probe plate is located on the thermalblock. The electrical connection can be disconnected for removal of thetemperature probe plate from the thermal cycler so that the temperatureprobe plate can be calibrated upon demand externally and separately fromthe thermal cycler.

Preferably the thermal cycler has a heated lid that can be closed. Inthe closed state the heated lid presses against the lids of the reactionor sample vessels and prevents condensation of water that has evaporatedfrom the reaction mixtures or test samples on the insides of the lids.

According to another embodiment of the invention the internal interfaceof the thermal cycler is connected to the probe plate by means of acable extending from the stowage compartment so that the probe plate canbe kept connected to the thermal cycler when it is within the stowagecompartment.

In order to keep the footprint of the thermal cycler as small aspossible the stowage compartment preferably has a slot-like form forinserting a narrow side of the probe plate into an opening of thecompartment while the temperature probes preferably project from a broadside of the probe plate as with conventional temperature probe plates.In order to avoid damaging the prevent the projecting temperature probesduring insertion or removal of the probe plate into/from the stowagecompartment the latter preferably comprises guiding means for guidingthe probe plate during insertion and removal.

According to another preferred embodiment of the invention thetemperature analysis and/or verification unit is connected to a displayon the housing by means of the internal interface. In this way thedisplay of the thermal cycler can be used for displaying the testresults from the temperature analysis and/or verification unit, all keythermal performance values or trend analysis without the need for anexternal display. Furthermore the display allows for a visual comparisonof the thermal cycler's thermal performance from test to test.Preferably the display is a touch-screen display that can be used tostart the temperature analysis and verification process and/or theself-calibration process.

According to a further preferred embodiment of the inventive method theanalysis and/or verification unit comprises a temperature probe platehaving a plurality of temperature probes for measuring the temperatureswithin selected sample wells of a thermal block of the thermal cyclerand in the further steps of disconnecting an electrical connectionbetween the temperature probe plate and the thermal cycler and removingthe temperature probe plate from the thermal cycler for separateexternal calibration of the temperature probe plate.

According to a further preferred embodiment of the inventive method, theintegrated analysis and/or verification unit comprises a temperatureprobe plate having a plurality of temperature probes for measuring thethermal performance of the thermal block within selected sample wells,wherein the temperature probes communicate temperature values to theelectronic control by means of an interface of the thermal cycler andwherein the electronic control compares the temperature values from thetemperature probes with target temperature values and initiates aself-calibration process of the thermal cycler when required. Preferablythe self-calibration process of the thermal cycler is in the form of aclosed-loop process using the temperature values communicated by thetemperature probes of the temperature analysis and/or verification unitfor modification of the performance of the electric heater means.

The present invention is illustrated by reference to the drawingfigures, encompassing different views of two embodiments of theinvention, wherein:

FIG. 1 is a schematic block diagram of the main components of a thermalcycler having an integrated temperature verification and calibrationunit according to the invention;

FIG. 2 is a perspective view of a preferred embodiment of a thermalcycler according to the invention with a temperature probe plate of thetemperature verification and calibration unit in a stowage compartmentof the thermal cycler;

FIG. 3 is a perspective view of the embodiment during removal of thetemperature probe plate from the stowage compartment;

FIG. 4 is a perspective view of the embodiment with the temperatureprobe plate in its position of use;

FIG. 4a is a detailed view of a portion of FIG. 4;

FIG. 5 is an enlarged top view of the stowage compartment during theremoval of the temperature probe plate as shown in FIG. 3;

FIG. 6 is an enlarged top view of the stowage compartment without thetemperature probe plate;

FIG. 7 is a perspective view of a temperature probe of the temperatureprobe plate;

FIG. 8 is a view of a screen of the thermal cycler after the start of atemperature verification and calibration software of the thermalcycler's temperature verification and calibration unit;

FIG. 9 is a view of the screen after the completion of a temperatureverification test conducted by the thermal cycler's temperatureverification and calibration unit;

FIG. 10 is a view of the screen when displaying thermal uniformity of athermal block of the thermal cycler against test date;

FIG. 11 is a perspective view of a second embodiment during removal ofthe temperature probe plate from the stowage compartment.

The thermal cycler 10 depicted in the drawings is used to amplifysegments of DNA via the polymerase chain reaction (PCR). Asschematically shown in FIG. 1 the thermal cycler 10 comprises a housing12 that accommodates a thermal block 14, a pivotable heated lid 16, eachcomprising an electric heater 18, 20, an electronic control 22 forcontrolling the electric heaters 18, 20 of the thermal block 14 and ofthe heated lid 16, a power supply 24, that is connected to the electricheaters 18, 20 through the electronic control 22, an internal singleboard computer and graphical interface 26, that is connected to theelectronic control 22 and to the power supply 24 and an integratedtemperature analysis and/or verification unit 28, that is connected tothe interface 26. As depicted in FIGS. 2 to 4 of the drawing at a frontof the housing 12 the thermal cycler 10 further comprises a display inthe form of a user-friendly colour touch-screen 30 with drag and dropfunction that is connected to the electronic control 22, the powersupply 24 and the internal interface 26. The thermal cycler furthercomprises a USB port (not shown) that is connected to the interface 26and facilitates the storage of programs from a USB memory stick in amemory of the electronic control.

The thermal block 14 is provided with an array of vertical holes orsample wells 32 as can be best seen from FIGS. 2 and 3. The sample wells32 are for receiving ninety six 0.2 ml sample or reaction tubes (notshown) or a 96-well PCR plate (not shown) that contain test samples orreaction mixtures to be tested. The thermal block 14 is removable sothat other block types, e.g. with three hundred and eighty four samplewells, can be fitted, if required.

The electric heater 18 of the thermal block 14 comprises eight Peltierelements (not shown) that assure an exact concordance between the actualtemperature of the thermal block 14 and a target temperature that isprovided by operating software stored in the memory of the electroniccontrol 22. The software controls the temperature of the thermal block14 that is raised and lowered in discrete, pre-programmed steps foralternately heating and cooling the test samples in the sample wells 32during the cycles of the PCR. The thermal block 14 is further providedwith four temperature control sensors (not shown) for measuring theactual temperature of the thermal block 14. The temperature controlsensors are connected with the electronic control 22.

In order to avoid any discrepancies or a temperature drift between theactual temperature measured by the temperature control sensors and theactual temperature within the sample wells 32 the temperature withinspecified sample wells 32 can be analyzed or verified with the help ofthe integrated temperature analysis and/or verification unit 28. Thetemperature analysis and/or verification unit 28 is used to perform avalidation and a verification of the temperature performance of thethermal block 14 in a way that is totally independent from thetemperature control of the thermal block 14 and other heated componentsof the thermal cycler, like the heated lid 16.

To this end the integrated temperature analysis and/or verification unit28 comprises a temperature probe plate 34 having a plurality oftemperature probes 36 and an embedded control electronics or computer(not shown) that may be either within the housing 12 of the thermalcycler 10 or within the temperature probe 34 plate itself. In the firstinstance the temperature probe plate 34 is electrically connected to thecontrol electronics or embedded computer through the internal interface26. In the second instance the control electronics or embedded computerwithin the temperature probe plate 34 is connected to the electroniccontrol 22 and the power supply 24 through the internal interface 26, sothat the temperature probe plate 34 is stand-alone, i.e. only requirespowering. The electric connection can be either temporary throughelectrical contacts 37, 39 or a plug-in connection when the temperatureprobe plate 34 is located on the thermal block 14, as shown in FIGS. 2to 4, so that the temperature probe plate 34 can be completely removedfrom the thermal cycler 10, e.g. for external calibration. Alternativelythe electrical connection can be permanent through a cable 38, as shownin FIG. 11.

The temperature probe plate 34 has a rectangular shape with two oppositebroad sides 40, 42 and four narrow sides. The dimensions of the broadsides 40, 42 essentially conform to the horizontal dimensions of thethermal block 14. The temperature probes 36 project from one 42 of thetwo broad sides 40, 42 of the temperature probe plate 34. The locationand size of the temperature probes 36 conforms to the location and sizeof the sample wells 32 so that they will fit into the sample wells whenthe temperature probe plate 34 is placed upon the thermal block 14, asshown in FIG. 4.

The temperature probes 36 are for sensing the temperature withinselected sample wells 32. As can be seen from FIG. 7, the temperatureprobes 36 essentially consist of a conical probe tip 46, a cylindricalprobe body 48 and a plug 50 at the end of the body 48 that is oppositefrom the probe tip 46. The probe tip 46 is made of a thermallyconductive material, shaped to match the well profile at the bottom ofthe samples wells 32, where the test sample or reaction mixture to betested is located during the normal operation of the thermal cycler 10,and houses a temperature sensor (not shown) that is electricallyconnected through the probe body 48 and the plug 50 to a circuitrywithin the temperature probe plate 34. The probe body 48 is made of athermally insulating material and designed to precisely position theprobe tip 46 at the bottom of the sample well 32 without draining heataway which would effect the temperature measurement of the temperaturesensor within the probe tip 46.

In the embodiments depicted in the drawing the temperature probes 36 arefixed to the temperature probe plate 34, so that they are immovable withrespect to the temperature probe plate 34 and are always associated withspecific sample wells 32. Preferably there are eight temperature probes36, which are considered a suitable number of probes to give adequatecoverage of the thermal block 14 in order to attain a representativemeasurement of its thermal uniformity.

However it can be contemplated to provide the temperature probe plate 34with a large number of sockets (not shown) on the broad side 42, so thatthe plug 50 of each temperature probe 36 can be optionally attached toan arbitrary one of the sockets. In this way the temperature probes 36are interchangeable and can be located in different sample wells 32.

If required, additional and differently shaped temperature probes 35 canbe added to the opposite broad side 40 of the temperature probe plate 34to allow for temperature measurement of the heated lid 16.

The temperature probe plate 34 is a calibrated piece of test equipment,traceable to national standards, and as such is known to be accurate.Due to the fact that the temperature probe plate 34 is completelyremovable from the thermal cycler 10 it can be itself calibrated orverified, independent from the thermal cycler 10.

The control electronics or embedded computer of the temperature analysisand/or verification unit 28 can comprise a separate processor and memorywithin the housing 12 of the thermal cycler 10 or within the temperatureprobe plate 34. Preferably the control electronics or embedded computeris within the temperature probe plate 34. The control electronics orembedded computer can be also part of the electronic control 22 whichshares its processor and memory with the embedded computer. The embeddedcomputer is used for performing temperature analysis or verificationprocesses, e.g. for processing temperature measurements, and, incooperation with the electronic control 22, self-calibration processesof the thermal cycler 10. To this end temperature analysis/verificationand self-calibration software is stored within a memory of the embeddedcomputer or within the shared memory.

In the preferred embodiment in FIGS. 2 to 4 the electrical connectionbetween the temperature probe plate 34 and the interface 26 is by meansof a plurality of electrical contact patches or protrusions 37 on thebroad side 40 of the temperature probe plate 34 and a correspondingplurality of mating contact patches 39 on a lower side 41 of the heatedlid 16 above the heated block 14. The contacts patches 37 and 39respectively are disposed in the same distance from a pivot axis of theheated lid 16 so that they are pressed against each other and are inelectrical contact when the temperature probe plate 34 is located on thethermal block 14 and when the heated lid 16 is pivoted on top of thebroad side 40 of the temperature probe plate 34 in its closed position.

In the embodiment in FIG. 11 the electrical connection is by means ofthe ribbon cable 38 having a plug 44 that can be connected to a matingsocket on one of the narrow sides of the temperature probe plate 34.

The function of the temperature probe plate 34 with the temperatureprobes 36 can be derived from FIGS. 2 to 4. In the normal operation ofthe thermal cycler 10 test samples or reaction mixtures are loaded intothe sample wells 32 and the temperature of the thermal block 14 israised and lowered in discrete, pre-programmed steps for alternatelyheating and cooling the test samples or reaction mixtures. During normaloperation, e.g. during the cycles of a PCR, the temperature analysisand/or verification unit 28 is not in use and no temperature analysisand/or verification is performed. As depicted in FIG. 2, during thattime the temperature probe plate 34 with the temperature probes 36 is ina stowage position within a stowage compartment 52. The stowagecompartment 52 is disposed between the thermal block 14 and the displayor screen 30 and is generally parallel to a back wall of the housing 12.The stowage compartment 52 has the form of a vertical slot for receivingthe temperature probe plate 34 in a vertical orientation with one of thenarrow sides facing downwardly. An opening 54 at the upper end of thestowage compartment 52 is flush with an upper surface of the housing 12between the thermal block 14 and the display or screen 30.

As can be seen best from FIGS. 5 and 6, the opening 54 of the stowagecompartment 52 is provided with a guide for guiding the temperatureprobe plate 34 during insertion into the slot-like compartment 52 andduring removal from the compartment 52. The guide comprises two verticalgrooves 56 that are located at the opposite ends of the elongatedopening 54 and of the compartment 52 and that receive two of the narrowsides of the temperature probe plate 34. In addition the guide comprisesa number of cutouts 58 in a lid 60 that covers the stowage compartment52 partially. The shape and location of the cutouts 58 conforms to theshape and location of the temperature probes 36 on the temperature probeplate 34 so that the temperature probes 36 will pass through the cutouts58. The lid 60 is provided with a further cut-out 61 for facilitatingthe removal of the temperature probe plate 34 from the stowage position.In an embodiment where the temperature probe plate 34 is provided withinterchangeable temperature probes 36 the lid 60 will be removed.

In the embodiment of FIG. 11 the ribbon cable 38 extends from the socketof the temperature probe plate 34 through the opening 54 to the bottomof the compartment 52, where it is connected to the interface 26.

When it is intended to measure the actual temperatures within the samplewells 32 in order to analyze or verify the thermal performance of thethermal cycler 10, i.e. of the thermal block 14 and the heated lid 16,the test samples or reaction mixtures are removed from the sample wells32 and the temperature probe plate 34 is removed from the stowagecompartment 52 and placed on the thermal block 14 with the temperatureprobes 36 within the specified sample wells 32, as shown in FIG. 4.

After that the analysis or verification process can be started bycalling an analysis/verification software routine on the touch-screen30, as shown in FIG. 8, and by touching the ok-button. Once the test iscomplete the user can instantly see on the screen 30 whether the thermaluniformity of the thermal block 14, the temperature accuracy, thetemperature overshoot and the timing, i.e. the thermal performance ofthe thermal cycler 10, are satisfactory, as shown in FIG. 9. The factthat the validation/verification of the temperature performance of thethermal block 14 performed by the temperature analysis and/orverification unit 28 is totally independent from the temperature controlof the thermal block 14 and of the heated lid 16 helps to ensure thatthe sensors in the thermal block 14 are functioning as intended and thatthe thermal cycler 10 as a whole can attain published specifications.Apart from displaying the thermal performance of the thermal cycler 10on its touch-screen 30 the thermal cycler can adjust its own performancedepending upon the results of the temperature measurements taken via thetemperature probe plate 34.

As exemplarily shown in FIG. 10 for thermal uniformity, the parametersof the thermal performance can be displayed against test time in orderto visualize thermal performance history of the thermal cycler 10. Ascan be seen from FIG. 10, the history records displayed on the screen 30comprise a base line or threshold barrier 62, so that the user caneasily see if any of thermal uniformity, temperature accuracy,temperature overshoot and/or timing of the thermal cycler 10 exceeds thebase line or threshold barrier 62 and therefore does not comply withrequirements. The history records displayed on the screen can also bestored on a USB-stick via the interface 26.

In order to check that it is functioning properly the thermal cycler 10will perform a quality control test upon demand when the temperatureprobe plate 34 is fitted to the thermal cycler 10. During this qualitycontrol test the thermal cycler 10 will step through a predeterminedthermal or temperature program and will simultaneously interrogate thetemperature probe plate 34 via the interface 26 in order to determinewhich temperatures are actually attained during the test. Thereafter thethermal cycler compares the actual temperature measurements against thetemperatures that were set or requested by the thermal cycler 10. Duringthis comparison any inaccuracies, i.e. differences between the actuallymeasured temperatures and the set temperatures, can be determined.

In order to avoid that one or more of thermal uniformity, temperatureaccuracy, temperature overshoot and timing exceed the associatedbaseline or threshold barrier 62 or to avoid the inaccuracies mentionedabove the thermal cycler 10 conducts a self-calibration process inregular time intervals, after each quality control test or upon demandby the user. During this self-calibration process a self-calibrationsoftware routine of the temperature analysis/verification andself-calibration software initiates a closed-loop process, where theactual or the last temperature values communicated from the temperatureprobes of the temperature probe plate 34 are compared with programmedtarget temperature values and where the temperature performance of thePeltier elements or electric heaters 18 of the thermal block 14 ismodified via the electronic control 22 in dependency from the differencebetween the actual/last temperature values and the target temperaturevalues.

In order to eliminate any inaccuracies furthermore the temperature probeplate 34 including all of its temperature probes 36 can be individuallyand externally calibrated by disconnecting the electrical contacts 37,39 or the plug-in connection between the temperature probe plate 34 andthe internal interface 26. During external calibration the temperatureprobes 36 of the temperature probe plate 34 are immersed in a circulatedoil bath and thermally calibrated to conform to national temperature ormeasurement standards. Thus it becomes possible not only to validate thethermal performance of the thermal cycler 10 but also to verify it inreadiness for performing a real experiment and to assure temperaturemeasurement accuracy. With other words it is possible to make sure thata predetermined setting of the temperature with the sample wells, e.g.95.0° C., is truly and precisely attained during the polymerase chainreaction (PCR), traceable to national standards.

The invention claimed is:
 1. A thermal cycler (10) comprising: a housing(12), the housing (12) accommodating a thermal block (14) having aplurality of sample wells (32), each for receiving a test sample in asample vessel, an electric heater means (18) for heating the thermalblock (14), a power supply (24), an electronic control (22) forcontrolling the electric heater means (18) and an internal interface(26), and a temperature analysis and verification unit (28) foranalyzing and verifying a thermal performance of the thermal block (14),wherein the temperature analysis and verification unit (28) comprises aremovable temperature probe plate (34) having a plurality of temperatureprobes (36) for measuring the temperature within selected sample wells(32), and wherein the temperature analysis and verification unit (28) isconnected to the power supply (24) and to the electronic control (22) bymeans of the internal interface (26), and an electric connection betweenthe temperature probe plate (34) and the internal interface (26) can bedisconnected for removal of the temperature probe plate (34) from thethermal cycler (10) for external calibration.
 2. The thermal cycleraccording to claim 1, wherein the temperature analysis and verificationunit (28) comprises a closed loop control for calibration of theelectric heater means (18) in dependency of the temperature measured bythe temperature probes (36) within selected sample wells (32).
 3. Thethermal cycler according to claim 1, wherein the temperature probe plate(34) is accommodated within a stowage compartment (52) of the housing(14) and is removable from the stowage compartment (52) for placement onthe thermal block (14).
 4. The thermal cycler according to claim 1,wherein the temperature probe plate (34) is accommodated within astowage compartment (52), and wherein the temperature probes (36)project from a broad side (42) of the temperature probe plate (34) andin that said stowage compartment (52) has a slot-like form for insertinga narrow side of the temperature probe plate (34) into an opening (54)of the stowage compartment (52).
 5. The thermal cycler according toclaim 4, wherein the opening (54) of the stowage compartment (52) islocated on top of the housing (14) close to said thermal block (14)having a plurality of sample wells (32).
 6. The thermal cycler accordingto claim 5, wherein the stowage compartment (52) comprises a guide,wherein said guide is configured to place the temperature probe plate(34) during insertion into the stowage compartment (52).
 7. The thermalcycler according to claim 6, wherein the temperature probe plate (34) isconnected to the internal interface (26) when a heated lid (16) of thethermal cycler (10) is closed.
 8. The thermal cycler according to claim7, wherein the temperature probe plate (34) is connected to the internalinterface (26) by at least one cable (38) that extends from thetemperature probe plate (34) into the stowage compartment (52).
 9. Thethermal cycler according to claim 8, wherein the temperature analysisand verification unit (28) is connected to a display (30) on the housing(12) by means of the internal interface (26).
 10. The thermal cycleraccording to claim 2 wherein the temperature probe plate (34) isaccommodated within a stowage compartment (52) of the housing (14) andis removable from the stowage compartment (52) for placement on thethermal block (14).
 11. The thermal cycler according to claim 2, whereinthe temperature probe plate (34) is accommodated within a stowagecompartment (52), and wherein the temperature probes (36) project from abroad side (42) of the temperature probe plate (34) and in that saidstowage compartment (52) has a slot-like form for inserting thetemperature probe plate (34) with a narrow side of the probe plate (34)facing an opening (54) of the stowage compartment (52).
 12. The thermalcycler according to claim 3 wherein the temperature probes (36) projectfrom a broad side (42) of the temperature probe plate (34) and in thatthe stowage compartment (52) has a slot-like form for inserting a narrowside of the temperature probe plate (34) into an opening (54) of thestowage compartment (52).
 13. The thermal cycler according to claim 11,wherein the opening (54) of the stowage compartment (52) is located ontop of the housing (14) close to said thermal block (14) having aplurality of sample wells (32).
 14. The thermal cycler according toclaim 12, wherein the opening (54) of the stowage compartment (52) islocated on top of the housing (14) close to said thermal block (14)having a plurality of sample wells (32).
 15. The thermal cycleraccording to claim 13, wherein the stowage compartment (52) comprises aguide, wherein said guide is configured to place the temperature probeplate (34) during insertion into the stowage compartment (52).
 16. Thethermal cycler according to claim 15, wherein the temperature probeplate (34) is connected to the internal interface (26) when a heated lid(16) of the thermal cycler (10) is closed.
 17. The thermal cycleraccording to claim 16, wherein the temperature probe plate (34) isconnected to the internal interface (26) by at least one cable (38) thatextends from the temperature probe plate (34) into the stowagecompartment (52).
 18. The thermal cycler according to claim 17, whereinthe temperature analysis and verification unit (28) is connected to adisplay (30) on the housing (12) by means of the internal interface(26).
 19. The thermal cycler according to claim 14, wherein the stowagecompartment (52) comprises a guide, wherein said guide is configured toplace the temperature probe plate (34) during insertion into the stowagecompartment (52).
 20. The thermal cycler according to claim 19, whereinthe temperature probe plate (34) is connected to the internal interface(26) when a heated lid (16) of the thermal cycler (10) is closed. 21.The thermal cycler according to claim 20, wherein the temperature probeplate (34) is connected to the internal interface (26) by at least onecable (38) that extends from the temperature probe plate (34) into thestowage compartment (52).
 22. The thermal cycler according to claim 21,wherein the temperature analysis and verification unit (28) is connectedto a display (30) on the housing (12) by means of the internal interface(26).